So far President Obama has steadfastly resisted even a modest involvement in the conflict, and there was no sign on Monday that a decision to use American force was imminent.

But Hezbollah’s large-scale entry into the fight in recent weeks and the Assad government’s firepower has tilted the battlefield in favor of the Syrian government.

“I think the rebels are in trouble,” said Jeffrey White, a former Middle East analyst with the Defense Intelligence Agency who is now a fellow at the Washington Institute for Near East Policy. “Speed is of the essence. The regime’s momentum needs to be brought to a halt.”

The NBC/WSJ poll was conducted May 30 to June 2 of 1,000 adults (including 300 cell phone-only respondents), and it has an overall margin of error of plus-minus 3.1 percentage points.